/*
 * 		Author : Xerxes
 * 		Program: 
 * 		Created On : 26.09.2011 10:21:37 BDT
 *      "I have not failed, I have just found 10000 ways that won't work.
 * 
*/


#include <iostream>
#include <algorithm>
#include <vector>
#include <sstream>
#include <fstream>
#include <string>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>

#include <ctime>
#include <cassert>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <climits>
#include <cstring>
#include <cstdlib>

using namespace std;

#define VI vector< int >
#define CI( x ) scanf("%d",&x)
#define CL( x ) scanf("%lld",&x)
#define CD( x ) scanf("%lf",&x )
#define fo(i,st,ed) for(int i = st ; i < ed ; ++i )
#define foE(i,st,ed) for(int i = st ; i <= ed ; ++i )
#define foit(i, x) for (typeof((x).begin()) i = (x).begin(); i != (x).end(); i++)
#define bip system("pause")
#define Int long long
#define pb push_back
#define SZ(X) (int)(X).size()
#define LN(X) (int)(X).length()
#define mk make_pair
#define f first
#define s second
#define SET( ARRAY , VALUE ) memset( ARRAY , VALUE , sizeof(ARRAY) )
#define tp pair< int, pair<int,int> >
#define mmk( x, y , z ) mk( x, mk( y, z ) )

inline void wait( double seconds ){
    double endtime = clock()+( seconds* CLOCKS_PER_SEC );
    while( clock() < endtime ){
        ;
    }
}
int K=1;
int N; 
int E; 
int u,v;
int sx,sy;
vector< vector<int> >go;
inline void Read(){
	CI(N);
	CI(E); 
	go.assign(N+5, vector<int>() );
	fo(i,0,E){
		CI(u);
		CI(v);
		go[u].pb(v);
		go[v].pb(u);
	}
	CI(sx);
	CI(sy);
}
int D[105][105];
const int inf = (int)1e5;

inline void bfs(int sx){
	queue< int > q;
	q.push( sx );
	D[sx][sx]=0;
	while( q.empty()==false ){
		int father = q.front();
		q.pop();
		
		vector< int > cango = go[father];
		for(int i=0,j=SZ(cango); i<j; ++i ){
			int child = cango[i];
			int nw_dist = D[sx][father]+1;
			if( nw_dist < D[sx][child] ){
				D[sx][child] = nw_dist;
				q.push( child );
			}
		}
	}
}
inline void Proc(){
	fo(i,0,105){
		fo(j,0,105){
			D[i][j]=inf;
		}
	}
	fo(i,0,N){
		bfs(i);
	}
	int best = 0;
	int prothom=1;
	fo(i,0,N){
		int current_best = D[sx][i] + D[i][sy];
		if( prothom ){
			prothom=0;
			best = current_best;
		}
		else{
			best = max( best, current_best );
		}
	}
	printf("Case %d: %d\n",K,best);
}
int main(){
    #ifndef ONLINE_JUDGE
        freopen("in","rt",stdin);
    #endif
    int cases=1;
    for( CI(cases) ; cases ; --cases,++K ){
        Read();
        Proc();
    }

return 0;
}


